The use of tamper-evident containers for consumer products including foods, beverages, pharmaceuticals, and the like deters any tampering with the products, and assures consumers that a package's contents are fresh and unadulterated. To this end, generally annular, heat-shrinkable tamper-evident seals are in widespread use in view of their economy and versatility. Seals of this nature typically comprise molecularly oriented plastic material which is subject to shrinkage upon heating. A shrinkable seal member is ordinarily fitted to a container after filling with product, with the member thereafter heated and shrunk into conformance with the container, typically so as to embrace the lid or other closure member of the container. In this manner, removal of the lid or other opening of the container requires fracturing and partial or complete removal of the tamper-evident seal, thus providing clear visual evidence of opening.
One particularly desirable type of heat-shrinkable seal member is disclosed in U.S. Pat. application Ser. No. 827,208, filed Feb. 4, 1986, now U.S. Pat. No. 4,691,835, with this type of seal desirably lending itself to high-speed manufacture and economical use. Economical use of this type of seal member is facilitated by the technique for applying the members to containers which is disclosed in U.S. Pat. No. 4,562,688, issued Jan. 7, 1986. Portions of the No. 4,562,688 patent document not inconsistent with the present disclosure are incorporated herein by reference.
While the seal member forming and applying techniques of the above patents are highly effective for forming tamper-evident containers and have proven commercially successful, the configuration of the particular type of container to which the seals are being applied can complicate the desired conformance of the seals to the containers. For example, many types of containers typically define a central, recessed region or area at the upper lid portion thereof. By way of example, containers used for different dairy products frequently include lid portions which define a central recess.
When fitting heat-shrinkable seal members to such containers, the seal member is typically positioned so as to encircle the lid portion and an adjacent region of the lower container portion, and is then heated so as to shrink inwardly into conformance with the container. Attendant to heat-shrinkage in this manner, the upper edge portion of the typically generally cylindrical seal contracts generally inwardly and downwardly during heating.
When completely shrunk, this edge portion of the seal is ordinarily inwardly oriented, and depending upon the dimensions of the seal and the container, may partially overlap or overlie the central recess in the container portion. While this ordinarily does not impair the function of the seal, this overlapping edge portion can permit dirt or other debris to undesirably become trapped and collect beneath the edge portion of the seal. Naturally, this can be unattractive, and detract from a product's consumer appeal, a particularly important consideration with regard to consumer food products and the like.
Accordingly, it is desirable to provide a technique for forming tamper-evident sealed containers, wherein heat-shrinkable seals applied to the containers are tightly conformed to the containers to obviate problems of debris being caught between the seals and the containers.